Effects of externally added Al₂O₃ and rare earth elements on microstructure and wear resistance of high-chromium cast iron

High-chromium cast iron has been widely applied in mining, metallurgy, building materials and other industries due to its eutectic carbides of the (Cr, Fe)₇C₃ type with high hardness in the microstructure. To regulate the morphology of eutectic carbides and improve the wear resistance of high-chromium cast iron, the master alloy method was adopted, Al₂O₃ particles were introduced into hypoeutectic high-chromium cast iron, and rare earth elements were added externally. The effects of these two additives on the microstructure and wear resistance of high-chromium cast iron were systematically compared. The results showed that after the introduction of Al₂O₃ particles, a small number of particles were distributed in the dendrite trunks, while most adhered to the surfaces of eutectic M₇C₃ carbides between dendrites. By virtue of the heterogeneous nucleation effect of Al₂O₃ particles, the secondary dendrite arm spacing of the high-chromium cast iron containing Al₂O₃ was reduced by 24% compared with that of the non-added sample, and the area fraction of eutectic M₇C₃ was increased by 3%. The carbide morphology was presented as short and fine plate-like, strip-like and rose petal-like shapes, and the secondary carbides were also significantly refined. In high-chromium cast iron containing rare earth elements, the secondary dendrite arm spacing and secondary carbide size showed little difference from those of the sample containing Al₂O₃, but the proportion of fine rose petal-like eutectics was as high as 12%. Wear resistance tests indicated that the friction coefficient of high-chromium cast iron with externally added Al₂O₃ during the wear process was 0.27, and the wear scar depth was (5.34±0.05) μm. The friction coefficient and wear scar depth were reduced by 61% and 70%, respectively, compared with those of conventional high-chromium cast iron. Its wear mechanism was transformed from fatigue wear to abrasive wear and adhesive wear.After the addition of rare earth elements, the friction coefficient of high-chromium cast iron was further reduced to 0.26, and the wear scar depth was decreased to (1.84±0.17) μm. This excellent performance was closely related to the high proportion of rose petal-like eutectic M₇C₃ in the material.